1. Field of the Invention
This invention pertains to ocean drilling platforms. More particularly, it pertains to a method of handling guidelines running from tensioners located on the drilling platform through a drill well to a submerged wellhead. This invention facilitates guideline handling as a blowout preventer is moved into position over and in the drill well prior to being lowered to the wellhead.
2. Review of the Prior Art
In drilling subsea oil or gas wells in the ocean from a floating structure, there comes a time in the drilling operation when a device known as a blowout preventer (BOP) is lowered to the ocean floor to be connected to the subsea wellhead. A riser pipe, which provides a return path to the drilling platform from the wellhead for flow of drilling mud and the like, or a drill string carrying a special BOP connecter at its lower end, is connected to the upper end of the BOP. The BOP is lowered into position on the wellhead through the agency of the riser or the drill string, as appropriate. As the BOP is lowered toward the wellhead, it is guided along guide cables which are connected to the wellhead structure already in place. After the BOP is installed, these guide cables are maintained in position to guide other equipment moved up and down toward the wellhead.
In the presently preferred embodiment of this invention, an air cushioned drilling platform is employed for oil exploration through the Arctic Ocean or on the tundra. Inasmuch as an air cushion drilling platform is substantially smaller than a conventional floating ocean drilling platform, space is at a premium. If the arrangement used on conventional ocean drilling platforms were used, the BOP could easily get fouled in the upper ends of the guidelines. A need exists for a solution for the problem of handling the guide cables as the blowout preventer is moved into place prior to lowering thereof to the well head through a central drill well of the platform.
The use of this invention in an air cushion drilling platform provides a simple and effective way to facilitate guideline handling which keeps the guidelines out of the way of the blowout preventer as it is moved into place over the drill well on its transfer cart and provides for proper positioning of the guidelines once the BOP is attached to the drilling string. These benefits may also be practiced advantageously on more conventional drilling platforms.